1. Field of the Invention
This invention relates to the control of plant growth and is particularly concerned with the use of certain fused cyclopentanones and cyclopentenones in the control of transpiration.
2. Description of the Related Art
There are many circumstances in which the use of plant growth retarding substances can be of considerable practical and economic significance, for example in control of the time of fruit ripening, bud sprouting or seed germination and in control of the extent of stem elongation (e.g. coleoptile growth). A further possible control is of transpiration via the stomatal apertures, thus giving control over the water balance of the plant. Control of the stomata, especially if reversible, can, for example, assist in the adaptation of crops to drought conditions and/or problems of salinity and alkalisation which may result from water shortage.
It has been known for some time that jasmonic acid and its simple carboxylic acid esters, eg methyl jasmonate, are involved in growth control. Thus Thimann et al (1979), Proc. Nat. Acad. Sci. USA, 716, 2295-2298 suggested that since methyl jasmonate is a volatile compound, it could be a volatile hormone involved in regulating the senescence and stomatal aperture of oat leaf segments. The formula (I) of methyl jasmonate is given below. ##STR2##
More recently, a review article by Parthier, J. Plant Growth Regulation (1990), 9, 57-63, in discussing the known stimulatory and inhibitory effects of jasmonic acid and methyl jasmonate, recounts the view that three important structural moieties are necessary for seedling growth inhibition (and probably for any biological activity): the acetoxy side chain, the n-pentenyl chain inserted at C-7, and a keto or hydroxy group at C-6.
It is against this background that a group of fused ring cyclopentanones and cyclopentenones have been found, which do not require all the structural features of methyl jasmonate or jasmonic acid and which surprisingly find application in the inhibition of transpiration.